There are more than 8,000 references in the literature on leptin. Nearly 6,000 of these references are from 2000 to the present, the remaining date back only to 1996. The discovery of this protein hormone has received great interest since leptin effects regulation of body weight, metabolism and reproductive function. This book is an edited collection beginning with the discovery of leptin and a study of its affect on animals and in humans. Chapters will focus on the discovery, history, roles and regulation of leptin in all the major areas of physiology, as well as on assay methods, phylogeny and genetics.